This invention relates to a lighting fixture and, more particularly, to an improved lighting fixture designed to project light uniformly distributed with a sharp cut-off above selected vertical angles and with the angle of the main beam projection and the angle above which the light is cut off adjustable.
Prior to the present invention, the most widely used lighting fixtures to provide directional light distribution were the industrial flood light and the prismatic unit. The industrial flood light permits the direction of the main beam to be adjusted, but does not provide any vertical cut-off. The prismatic unit reduces the amount of light which escapes at excessively high angles over that of the flood light, but it provides no sharp vertical cut-off and, in the prismatic unit, the vertical angle at which the main beam is projected is fixed and cannot be adjusted. In both the prismatic unit and the flood light, large amounts of light are allowed to escape at excessively high angles. This misdirected light is not only wasteful but is ecologically undesirable and highly detrimental to area visibility because of the glare that it produces. In addition, the lack of a cut-off angle in the flood light or a sharp cut-off angle in the prismatic unit will result in light trespass, which is unwanted illumination of surrounding areas.
The lighting fixture of the present invention improves dramatically on both of these prior art fixtures by providing a sharp cut-off angle with little wasted light and with relatively uniform light distribution over the illuminated area. The angle of the main beam of projection from the fixture from vertical is readily adjustable as is the vertical cut-off angle and this adjustment can be done without changing the position of the housing or lens of the fixture so that the lighting fixture has the same position as viewed externally for different vertical angles of projection and cut-off. Moreover, the preferred embodiment of the fixture produces a uniform horizontal distribution extending around the fixture and operates to provide some illumination behind the aperture of the fixture through which the light is projected so that when the fixture is mounted externally on a wall, illumination will be provided on the wall.
These advantages of the present invention are achieved by means of a reflector system which surrounds the light source having a generally cylindrical concave curvature above the fixture and having a parabolic curvature concave in two directions below the fixture. The specific shape of the reflector is selected to give the sharp vertical cut-off, to provide relatively uniform distribution of the light over the illuminated area, and spread the distribution of the light. The light is projected through an aperture in the housing in which is mounted a specially shaped lens projecting from the aperture. The lens serves to increase the uniformity of the distribution of the light and direct some of the projected light back behind the aperture. The lens provides the ribs on the vertically extending walls thereof so as to provide the desired distribution of the light through horizontal angles without interferring with the vertical cut-off of the fixture or the vertical distribution which is achieved by the reflector system. Near the top of the aperture, a second reflector is provided with a flat middle portion and with two ears projecting perpendicularly therefrom on either side of the arc tube of the lamp. The ears of this reflector provide for increased sideways illumination from the fixture and the flat middle portion serves to provide an image of the arc tube near the top of the aperture.
The reflector system, along with the lamp, is pivotally adjustable within the housing. This adjustment causes vertical adjustment of the main beam from the fixture and also will adjust the vertical cut-off angle. The angular adjustment causes the lamp to move back or forward in the housing. When the lamp is moved toward the back of the housing to provide higher angles of projection, the lamp would be moved too far away from the front of the fixture to provide good lateral distribution of light from the fixture. The auxilliary reflector mounted at the top of the aperture providing an image of the arc tube at this position serves to provide lateral distribution of light when the lamp is pivoted to the back of the housing.